Composition for Encapsulant Film Comprising Ethylene/Alpha-Olefin Copolymer and Encapsulant Film Comprising the Same

ABSTRACT

The present invention relates to a composition for an encapsulant film, including an ethylene/alpha-olefin copolymer having high volume resistance and light transmittance, and an encapsulant film using the same.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Korean Patent Application No. 2020-0046029, filed on Apr. 16, 2020, in the Korean Intellectual Property Office, the contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a composition for an encapsulant film including an ethylene/alpha-olefin copolymer having high volume resistance and light transmittance, and an encapsulant film using the same.

BACKGROUND ART

As global environmental problems, energy problems, etc. get worse and worse, solar cells receive attention as a clean energy generating means without fear of exhaustion. If solar cells are used outside such as the roof of a building, generally, a module type is used. In order to obtain a crystalline solar cell module when manufacturing a solar cell module, protection sheet for solar cell module (surface side protection member)/solar cell sealant/crystalline solar cell device/solar cell sealant/protection sheet for solar cell module (back side protection member) are stacked in order. Meanwhile, in order to manufacture a thin film-based solar cell module, thin film-type solar cell device/solar cell sealant/protection sheet for solar cell module (back side protection member) are stacked in order.

As the solar cell sealant, generally, an ethylene/vinyl acetate copolymer or ethylene/alpha-olefin copolymer, etc. is used. In addition, in the solar cell sealant, a light stabilizer is generally included as an additive considering the requirement on climate-resistance for a long time. In addition, considering the adhesiveness of a transparent surface side protection member or a back side protection member represented by glass, a silane coupling agent is commonly included in the solar cell sealant.

Particularly, an ethylene/vinyl acetate copolymer (EVA) sheet has been widely used because transparency, flexibility and adhesiveness are excellent. An ethylenevinyl acetate copolymer (EVA) film has been widely used because transparency, flexibility and adhesiveness are excellent. However, if an EVA composition is used as the constituent material of a solar cell sealant, it has been apprehended that components such as an acetic acid gas generated by the decomposition of EVA might influence a solar cell device.

In addition, the increase of the scale of a power generation system such as a mega solar is conducted along with the recent dissemination of the power generation of the sunlight, and for the purpose of reducing transmission loss, there are moves to increase a voltage of a system voltage. As the system voltage increases, a potential difference between a frame and cells increases in a solar cell module. That is, the frame of a solar cell module is generally grounded, and if the system voltage of a solar cell array is from 600 V to 1000 V, the potential difference between the frame and the cells becomes from 600 V to 1000 V just the same in a module with the highest voltage, and the power generation is maintained during the day in a high-voltage applied state. In addition, glass has lower electric resistance when compared with a sealant, and due to the interposition of the frame, a high voltage is generated between the glass and the cells. That is, under the circumstance of generating power during the day, in a module with series connection, a potential difference between the cells and the module, and the cells and glass side increases in succession from a grounded side, and at the greatest point, almost the same potential difference of the system voltage is maintained. In a solar cell module used in such a state, output is largely reduced, and an example of a module using a crystalline power generation device in which potential induced degradation (abbreviated as PID) phenomenon arising degradation is generated, has been reported. Accordingly, in order to solve the problems, a solar cell sealant which comes into direct contact with the solar cell device, having even higher volume intrinsic resistance is required.

Volume resistance or specific resistance (p) known as electric resistance is defined as electric resistance between facing surfaces of 1 m³ of a material, and it is importance to obtain a molded article in which this volume resistance may be reproduced in a predetermined range in all application divisions and permanent. In an electric insulation material field for a high-voltage power cable, low-density polyethylene processed at a high pressure, crosslinked polyethylene, etc. are widely used due to excellent electric properties. One of the difficulties of the high-voltage power cable is the power loss shown during power transmission. The reduction of the power loss is the most important conditions to be satisfied. The reduction of the power loss could be attained by increasing the high-voltage properties, particularly, volume resistance of an insulating material. However, in the insulating material for a power cable, the inner part of a conductor is heated to a high temperature (about 90° C.) by heat generated by the passing of current, but the outer part of the conductor maintains room temperature. The conventional polyethylene shows marked drop of volume resistance according to the increase of the temperature. Accordingly, polyethylene shows marked drop of volume resistance near the inner conductor through the passing of current.

As described above, the development of an ethylene/alpha-olefin copolymer usefully utilized as a material having excellent volume resistance and requiring high insulation such as a solar cell encapsulant is still required.

PRIOR ART DOCUMENT Patent Document

Korean Laid-open Patent No. 2018-0063669

DISCLOSURE OF THE INVENTION Technical Problem

An object of the present invention is to provide a composition for an encapsulant film showing high volume resistance and excellent insulation by including an ethylene/alpha-olefin copolymer maintaining a narrow degree of molecular weight distribution and showing high crystallinity distribution.

Another object of the present invention is to provide a method for preparing the composition for an encapsulant film and an encapsulant film manufactured using the composition for an encapsulant film.

Technical Solution

To solve the above tasks, the present invention provides a composition for an encapsulant film including an ethylene/alpha-olefin copolymer satisfying the following conditions (a) to (d):

(a) a density is 0.85 to 0.89 g/cc;

(b) molecular weight distribution is 1.5 to 2.3;

(c) a melting temperature is 85° C. or less; and

(d) a free volume proportional constant (C₂) derived from the following Equations 1 and 2 is 600 or less:

$\begin{matrix} {{\log\frac{\eta_{0}(T)}{\eta_{0}\left( T_{r} \right)}} = {\log\left( a_{T} \right)}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack \end{matrix}$

in Formula 1,

η₀(T) is a viscosity (Pa·s) of a copolymer measured at an arbitrary temperature of T (K) using ARES-G2 (Advanced Rheometric Expansion System),

η₀ (T_(r)) is a viscosity (Pa·s) of a copolymer measured at a reference temperature of T_(r) (K) using the ARES-G2, and

a_(T) is a shift factor of the arbitrary temperature of T (K) with respect to the reference temperature of T_(r) (K), and obtained from Equation 1 above,

$\begin{matrix} {{\log\left( a_{T} \right)} = \frac{- {C_{1}\left( {T - T_{r}} \right)}}{C_{2}\left( {T - T_{r}} \right)}} & \left\lbrack {{Equation}\mspace{14mu} 2} \right\rbrack \end{matrix}$

in Formula 2,

C₁ is a free volume inverse proportional constant,

C₂ is a free volume proportional constant (K), and

C₁ and C₂ are intrinsic constants of the ethylene/alpha-olefin copolymer, and obtained from Equation 2 above.

In addition, the present invention provides an encapsulant film including the composition for an encapsulant film.

Advantageous Effects

The composition for an encapsulant film of the present invention utilizes an ethylene/alpha-olefin copolymer having high crystallinity distribution and a small free volume, and shows excellent volume resistance and light transmittance, and accordingly, may be widely used for various uses in electric and electronic industrial fields.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described in more detail to assist the understanding of the present invention.

It will be understood that words or terms used in the present disclosure and claims shall not be interpreted as the meaning defined in commonly used dictionaries. It will be further understood that the words or terms should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the technical idea of the invention, based on the principle that an inventor may properly define the meaning of the words or terms to best explain the invention.

[Ethylene/Alpha-Olefin Copolymer]

The composition for an encapsulant film of the present invention is characterized in including an ethylene/alpha-olefin copolymer satisfying the following conditions (a) to (d):

(a) a density is 0.85 to 0.89 g/cc;

(b) molecular weight distribution is 1.5 to 2.3;

(c) a melting temperature is 85° C. or less; and

(d) a free volume proportional constant (C₂) derived from the following Equations 1 and 2 is 600 or less:

$\begin{matrix} {{\log\frac{\eta_{0}(T)}{\eta_{0}\left( T_{r} \right)}} = {\log\left( a_{T} \right)}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack \end{matrix}$

in Formula 1,

η₀(T) is a viscosity (Pa·s) of a copolymer measured at an arbitrary temperature of T (K) using ARES-G2 (Advanced Rheometric Expansion System),

η₀(T_(r)) is a viscosity (Pa·s) of a copolymer measured at a reference temperature of T_(r) (K) using the ARES-G2, and

a_(T) is a shift factor of the arbitrary temperature of T (K) with respect to the reference temperature of T_(r) (K), and obtained from Equation 1 above,

$\begin{matrix} {{\log\left( a_{T} \right)} = \frac{- {C_{1}\left( {T - T_{r}} \right)}}{C_{2}\left( {T - T_{r}} \right)}} & \left\lbrack {{Equation}\mspace{14mu} 2} \right\rbrack \end{matrix}$

in Formula 2,

C₁ is a free volume inverse proportional constant,

C₂ is a free volume proportional constant (K), and

C₁ and C₂ are intrinsic constants of the ethylene/alpha-olefin copolymer, and obtained from Equation 2 above.

The present invention relates to a composition for an encapsulant film showing high volume resistance and showing excellent electrical insulation. Particularly, for preparing an ethylene/alpha-olefin copolymer included in the composition for an encapsulant film of the present invention, transition metal compounds represented by Formula 1 and Formula 2 are mixed and used as a catalyst. The introduction of an alpha-olefin-based monomer into the transition metal compound represented by Formula 1 is difficult due to the structural characteristics of the catalyst, and a copolymer of a high-density region tends to be prepared, and a large amount of alpha-olefin may be introduced into the transition metal compound represented by Formula 2, a polymer (elastomer) in a very low-density region may be prepared. Accordingly, if each of the two transition metal compounds is used solely, copolymerization properties of mixing and introducing an alpha-olefin-based monomer are different.

The ethylene/alpha-olefin copolymer prepared by using the mixture composition as a catalyst is a copolymer in which both a low-density region in which a large amount of an alpha-olefin-based monomer is mixed and introduced and a high-density region in which a small amount of an alpha-olefin-based monomer is mixed and introduced are present, and has wide crystallinity distribution, and contains a small free volume. Accordingly, the composition for an encapsulant film of the present invention using the same has low charge mobility and shows excellent electric insulation.

The ethylene/alpha-olefin copolymer included in the composition for an encapsulant film of the present invention is a polymer having a low density in a range of 0.85 to 0.89 g/cc, and in this case, the density may mean a density measured according to ASTM D-792. More particularly, the density may be 0.850 g/cc or more, 0.860 g/cc or more, 0.870 g/cc or more, 0.875 g/cc or more, and 0.890 g/cc or less, or 0.880 g/cc or less.

If the density deviates from the range, problems of degrading the volume resistance or light transmittance of the ethylene/alpha-olefin copolymer may arise.

Generally, the density of the ethylene/alpha-olefin copolymer is influenced by the type and amount of a monomer used for polymerization, a polymerization degree, etc., and is largely influenced by the amount of a comonomer in case of a copolymer. In this case, if the amount of the comonomer increases, an ethylene/alpha-olefin copolymer of a low density may be prepared, and the amount of the comonomer introduced into the copolymer may be dependent on the intrinsic copolymerization properties of a catalyst.

The ethylene/alpha-olefin copolymer included in the composition for an encapsulant film of the present invention is a copolymer prepared using the compounds represented by Formula 1 and Formula 2 as catalysts, and shows a low density as described above, and as a result, excellent processability may be shown.

The ethylene/alpha-olefin copolymer included in the composition for an encapsulant film of the present invention has narrow molecular weight distribution (MWD) in a range of 1.5 to 2.3. More particularly, the molecular weight distribution may be 1.50 or more, 1.80 or more, or 1.90 or more, and 2.30 or less, 2.20 or less, 2.15 or less, or 2.00 or less.

Generally, if two or more types of monomers are polymerized, molecular weight distribution increases, and as a result, impact strength and mechanical properties are reduced, and there is possibility of generating blocking phenomenon, etc. Particularly, since the polymerization properties of a monomer are different according to the catalyst, the molecular weight of a polymer finally prepared may be influenced by the type of the catalyst. If two or more types of catalysts are mixed and used in polymerization reaction, and if the difference of the polymerization properties of the catalysts is large, there are problems of increasing the molecular weight distribution of a polymer.

In order to reduce the molecular weight distribution to prevent the degradation of the crosslinking properties, impact strength, mechanical properties, etc. of a copolymer, a suitable amount of hydrogen may be injected during polymerization reaction to prevent the generation of arbitrary β-hydride elimination reaction in a polymer chain and induce uniform termination reaction, and in this case, the weight average molecular weight and melt index of the copolymer tend to decrease according to the injection of hydrogen. Accordingly, appropriate catalyst type and hydrogen injection amount are determined in ranges for achieving both the intrinsic properties of a catalyst structure influencing the weight average molecular weight and the melt index and the reducing effects of molecular weight distribution according to the injection of hydrogen.

Considering the above-described points, in the present invention, since a transition metal compound represented by Formula 1 and a transition metal compound represented by Formula 2 are mixed and used as a catalyst, an excellent ethylene/alpha-olefin copolymer having the above-described range of narrow molecular weight distribution and satisfying other physical properties may be prepared.

In addition, the ethylene/alpha-olefin copolymer included in the composition for an encapsulant film of the present invention may have a weight average molecular weight (Mw) of 40,000 g/mol to 150,000 g/mol. Particularly, the weight average molecular weight may be 45,000 g/mol or more, 49,000 g/mol or more, or 52,000 g/mol or more, and 130,000 g/mol or less, 90,000 g/mol or less, or 65,000 g/mol or less.

The weight average molecular weight (Mw) and the number average molecular weight (Mn) are polystyrene conversion molecular weights analyzed by gel permeation chromatography (GPC), and the molecular weight distribution may be calculated from the ratio of Mw/Mn.

The ethylene/alpha-olefin copolymer included in the composition for an encapsulant film of the present invention has a melting temperature (Tm) of 85° C. or less. Particularly, the melting temperature may be 50° C. or more, 55° C. or more, or 60° C. or more, and 85° C. or less, 70° C. or less, 68° C. or less, or 65° C. or less.

Generally, if the crystallinity distribution of a copolymer is high, the high crystal content increases, and the degradation of light transmittance and crosslinking physical properties may be induced. On the contrary, the copolymer of the present invention has wide crystallinity distribution, high volume resistance and a low melting temperature as described above, and accordingly, there are advantages in that light transmittance and crosslinking physical properties are not deteriorated.

At the same time, the ethylene/alpha-olefin copolymer of the present invention may have a crystallization temperature (Tc) of 70° C. or less, 60° C. or less, 50° C. or less, or 49° C. or less, and 30° C. or more, 35° C. or more, 40° C. or more, 45° C. or more.

The melting temperature and crystallization temperature may be measured using differential scanning calorimeter (DSC). Particularly, a copolymer is heated to 150° C. and maintained for 5 minutes, and the temperature is reduced to −100° C. again and elevated again. In this case, the elevating rate and decreasing rate of the temperature are controlled to 10° C./min, respectively. Measured results in the second temperature elevating section is the melting temperature, and the measured results in a range shown while reducing the temperature is the crystallization temperature.

The ethylene/alpha-olefin copolymer included in the composition for an encapsulant film of the present invention has a free volume proportional constant of C₂ derived from Equations 1 to 3 of 600 or less, and in this case, the unit of C₂ is absolute temperature (K). More particularly, the free volume proportional constant (C₂) may be 600 or less, 550 or less, or 500 or less, and 300 or more.

The physical/chemical properties of a polymer such as an ethylene/alpha-olefin copolymer are considered to be fixed, but in practice, have properties dependent on time and temperature. If viscoelastic functional curves in accordance with time at various temperatures are derived and moved horizontally in parallel based on an arbitrary temperature, time-temperature superposition is shown by which all curves are superposed into one curve.

In this case, the relation of Equation 1 below is established for data of physical properties on arbitrary temperature T (kelvin, K) and reference temperature T_(r) (Kelvin, K) with respect to data of linear viscoelasticity of a copolymer measured at various temperatures. In equation 1, η₀(T) is a viscosity (Pa·s) of a copolymer measured at an arbitrary temperature of T (K) using ARES-G2, and η₀(T_(r)) is a viscosity (Pa·s) of a copolymer measured at a reference temperature of T_(r)(K) using ARES-G2. From the above, a shift factor (a_(T), a factor of shifting the phase of a graph for anticipating data of physical properties measured at the temperature of T as data of physical properties at another temperature) of the arbitrary temperature of T (K) with respect to the reference temperature of T_(r)(K) may be obtained, and this represents temperature dependency.

$\begin{matrix} {{\log\frac{\eta_{0}(T)}{\eta_{0}\left( T_{r} \right)}} = {\log\left( a_{T} \right)}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack \end{matrix}$

In addition, it has been found that the shift factor (a_(T)) making data of physical properties at all temperatures superposed into one curve has a mathematical form below, and this is called Williams-Landel-Ferry equation (WLF equation).

$\begin{matrix} {{\log\left( a_{T} \right)} = \frac{- {C_{1}\left( {T - T_{r}} \right)}}{C_{2}\left( {T - T_{r}} \right)}} & \left\lbrack {{Equation}\mspace{14mu} 2} \right\rbrack \end{matrix}$

In Formula 2, C₁ is a free volume inverse proportional constant, C₂ is a free volume proportional constant (K), and C₁ and C₂ are intrinsic constants of the ethylene/alpha-olefin copolymer, and obtained from Equation 2 above.

In the present invention, C₁ may be a value of 2 or more, 3 or more, and 7 or less, 5 or less, but is not limited thereto.

More particularly, in the present invention, a process of obtaining the C₂ value may be as follows using a measurement apparatus of ARES-G2 (Advanced Rheometric Expansion System) of TA Co. Particularly, a disk type disk specimen of an ethylene/alpha-olefin copolymer having a diameter of 25 mm and a thickness of 1 mm was prepared as a sample. The geometry of a parallel plate (flat shape) was used, and Equation 1 was calculated by the methods 1) and 2) below.

1) Frequency Sweep at Five Specific Temperatures

In a temperature range lower than Tg+200° C. of an ethylene/alpha-olefin copolymer, frequency sweep was measured at five specific temperatures selected with an interval of 10° C. In the present invention, measurement was conducted at a temperature of 110-150° C. with an interval of 10° C. (strain 0.5-3%, frequency 0.1-500 rad/s).

2) Deduction of Master Curve

The reference temperature T_(r) was set to 130° C., and the measurement results of step 1) was shifted to 130° C. to deduce a master curve.

3) Deduction of C₂ Value

The shift factor (aT) of a WLF equation was obtained, and this value was substituted in Equation 2 to deduce a C₂ value.

$\begin{matrix} {C_{2} = \frac{f_{0}}{\alpha_{f}}} & \left\lbrack {{Equation}\mspace{14mu} 3} \right\rbrack \end{matrix}$

As in Equation 3, the C₂ value is a value proportional to a free volume (f₀), and a small C₂ means a small free volume in a copolymer, and in this case, α_(f) means a coefficient of thermal expansion of an ethylene/alpha-olefin copolymer.

In addition, the ethylene/alpha-olefin copolymer included in the composition for an encapsulant film has a melt index (MI, 190° C., 2.16 kg load conditions) of 0.1 to 50 dg/min. More particularly, the melt index may be 1 dg/min or more, 1.5 dg/min or more, 3 dg/min or more, or 4 dg/min or more, and 50 dg/min or less, 30 dg/min or less, 20 dg/min or less, or 10 dg/min or less.

In addition, the ethylene/alpha-olefin copolymer included in the composition for an encapsulant film may have a melt flow rate ratio (MFRR, MI₁₀/MI_(2.16)) which is a value of melt index (MI₁₀, 190° C., 10 kg load conditions) with respect to the melt index (MI_(2.16), 190° C., 2.16 kg load conditions), of 8.0 or less, 7.0 or less, or 6.5 or less, or 6.3 or less and 5.0 or more, or 5.5 or more, or 6.0 or more.

The melt flow rate ratio is an index of the degree of long chain branching of a copolymer, and the ethylene/alpha-olefin copolymer of the present invention satisfies the melt flow rate ratio together with the above-described physical properties and has excellent physical properties, and thus, may be suitably applied to an encapsulant composition for a solar cell.

The ethylene/alpha-olefin copolymer is prepared by copolymerizing ethylene and an alpha-olefin-based monomer, and in this case, the alpha-olefin which means a moiety derived from an alpha-olefin-based monomer in the copolymer may be C4 to C20 alpha-olefin, particularly, propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, 1-octene, 1-decene, 1-undecene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-eicosene, etc., and any one among them or mixtures of two or more thereof may be used.

Among them, the alpha-olefin may be 1-butene, 1 hexene or 1-octene, preferably, 1-butene, 1-hexene, or a combination thereof.

In addition, in the ethylene/alpha-olefin copolymer, the alpha-olefin content may be suitably selected in the range satisfying the physical conditions, particularly, greater than 0 to 99 mol %, or 10 to 50 mol %, without limitation.

In addition, by using the composition for an encapsulant film of the present invention, a modified resin composition, for example, a silane modified resin composition or an amino silane modified resin composition may be prepared.

Particularly, the composition for an encapsulant film may include a known crosslinking agent, crosslinking auxiliary agent, silane coupling agent, etc., in addition to the ethylene/alpha-olefin copolymer.

The crosslinking agent is a radical initiator in the preparation step of the silane modified resin composition, and may play the role of initiating graft reaction of an unsaturated silane composition onto a resin composition. In addition, by forming a crosslinking bond in the silane modified resin composition, or between the silane modified resin composition and an unmodified resin composition during a lamination step for manufacturing an optoelectronic device, the heat resistant durability of a final product, for example, an encapsulant sheet may be improved.

The crosslinking agent may use various crosslinking agents well-known in this technical field only if it is a crosslinking compound capable of initiating the radical polymerization of a vinyl group or forming a crosslinking bond, for example, one or two or more selected from the group consisting of organic peroxides, hydroxyl peroxides and azo compounds.

Particularly, one or more selected from the group consisting of dialkyl peroxides such as t-butylcumylperoxide, di-t-butyl peroxide, di-cumyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, and 2,5-dimethyl-2,5-di(t-butylperoxy)-3-hexyne; hydroperoxides such as cumene hydroperoxide, diisopropyl benzene hydroperoxide, 2,5-dimethyl-2,5-di(hydroperoxy)hexane, and t-butyl hydroperoxide; diacyl peroxides such as bis-3,5,5-trimethylhexanoyl peroxide, octanoyl peroxide, benzoyl peroxide, o-methylbenzoyl peroxide, and 2,4-dichlorobenzoyl peroxide; peroxy esters such as t-butylperoxy isobutyrate, t-butylperoxy acetate, t-butylperoxy-2-ethylhexylcarbonate (TBEC), t-butylperoxy-2-ethylhexanoate, t-butylperoxy pyvalate, t-butylperoxy octoate, t-butylperoxyisopropyl carbonate, t-butylperoxybenzoate, di-t-butylperoxyphthalate, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, and 2,5-dimethyl-2,5-di(benzoylperoxy)-3-hexyne; ketone peroxides such as methyl ethyl ketone peroxide and cyclohexanone peroxide, lauryl peroxide, and azo compounds such as azobisisobutyronitrile and azobis(2,4-dimethylvaleronitrile), may be used, without limitation.

The organic peroxide may be an organic peroxide having a one-hour half-life temperature of 120 to 135° C., for example, 120 to 130° C., 120 to 125° C., preferably, 121° C. The “one-hour half-life temperature” means a temperature at which the half-life of the crosslinking agent becomes one hour. According to the one-hour half-life temperature, the temperature at which radical initiation reaction is efficiently performed may become different. Therefore, in case of using the organic peroxide having the one-hour half-life temperature in the above-described range, radical initiation reaction, that is, crosslinking reaction in a lamination process temperature for manufacturing an optoelectronic device may be effectively performed.

The crosslinking agent may be included in 0.01 to 1 parts by weight, for example, 0.05 to 0.55, 0.1 to 0.5 or 0.15 to 0.45 parts by weight based on 100 parts by weight of the composition for an encapsulant film. If the crosslinking agent is included in less than 0.01 parts by weight, heat resistant properties may be insignificant, and if the amount is greater than 1 part by weight, the moldability of an encapsulant sheet is deteriorated, problems generating process limitation may arise, and physical properties of an encapsulant may be influenced.

In addition, the resin composition may include a crosslinking auxiliary agent in addition to the crosslinking agent. By including the crosslinking auxiliary agent in the resin composition, the crosslinking degree in the resin composition by the crosslinking auxiliary agent may be increased, and accordingly, the heat resistant durability of a final product, for example, an encapsulant sheet may be improved even further.

The crosslinking auxiliary agent may use various crosslinking auxiliary agents well-known in this technical field. For example, as the crosslinking auxiliary agent, a compound containing at least one or more unsaturated groups such as an allyl group and a (meth)acryloxy group may be used.

The compound containing the allyl group may include, for example, a polyallyl compound such as triallyl isocyanurate (TAIC), triallyl cyanurate, diallyl phthalate, diallyl fumarate and diallyl maleate, and the compound containing the (meth)acryloxy group may include a poly(meth)acryloxy compound such as ethylene glycol diacrylate, ethylene glycol dimethacrylate, and trimethylolpropane trimethacryate, without limitation.

The crosslinking auxiliary agent may be included in an amount of 0.01 to 0.5 parts by weight, for example, 0.01 to 0.3, 0.015 to 0.2, or 0.016 to 0.16 parts by weight based on 100 parts by weight of the composition for an encapsulant film. If the crosslinking auxiliary agent is included in less than 0.01 parts by weight, the improving effects of heat resistant properties may be insignificant, and if the amount is greater than 0.5 parts by weight, problems of affecting the physical properties of a final product, for example, an encapsulant sheet may be generated, and the production cost may increase.

In addition, the composition for an encapsulant film may additionally include a silane coupling agent in addition to the ethylene/alpha-olefin copolymer, the crosslinking agent and the crosslinking auxiliary agent.

The silane coupling agent may use, for example, one or more selected from the group consisting of N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane, N-(β-aminoethyl)-γ-aminopropylmethyldimethoxysilane, γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, and γ-methacryloxypropyltrimethoxysilane (MEMO).

The silane coupling agent may be included in 0.1 to 0.4 parts by weight based on 100 parts by weight of the composition for an encapsulant film. If the amount used is less than 0.3, adhesiveness with glass during manufacturing a solar cell module may become poor, and water penetration may become easy, and thus, the long-term performance of the module may not be secured. If the amount is more than 1 part by weight, it acts as an increasing factor of Y.I, undesirably.

In addition, the composition of an encapsulant film may additionally include an unsaturated silane compound and an amino silane compound.

The unsaturated silane compound may be grafted into a main chain including the polymerization unit of the monomer of the copolymer of the present invention in the presence of a radical initiator, etc., and included in a polymerized type in a silane modified resin composition or an amino silane modified resin composition.

The unsaturated silane compound may be vinyltrimethoxy silane, vinyltriethoxy silane, vinyltripropoxy silane, vinyltriisopropoxy silane, vinyltributoxy silane, vinyltripentoxy silane, vinyltriphenoxy silane, or vinyltriacetoxy silane, and in an embodiment, vinyltrimethoxy silane or vinyltriethoxy silane may be used among them, without limitation.

In addition, the amino silane compound may act as a catalyst for promoting hydrolysis reaction for converting an unsaturated silane compound grafted in the main chain of the copolymer, for example, a reactive functional group such as the alkoxy group of vinyltriethoxy silane into a hydroxyl group in the grafting modification step of the ethylene/alpha-olefin copolymer, to improve the adhesive strength of upper and lower glass substrates or with a back sheet composed of a fluorine resin, etc. At the same time, the amino silane compound may be directly involved as a reactant in copolymerization reaction and may provide an amino modified resin composition with a moiety having an amine functional group.

The amino silane compound is a silane compound including an amine group and is not specifically limited as long as it is a primary amine or a secondary amine. For example, the amino silane compound may use aminotrialkoxysilane, aminodialkoxysilane, etc., and examples may include one or more selected from the group consisting of 3-aminopropyltrimethoxysilane (APTMS), 3-aminopropyltriethoxysilane (APTES), bis[(3-triethoxysilyl)propyl]amine, bis[(3-trimethoxysilyl)propyl]amine, 3-aminopropylmethyldiethoxysilane, 3-aminopropylmethyldimethoxysilane, N-[3-(trimethoxysilyl)propyl]ethylenediamine (DAS), aminoethylaminopropyltriethoxysilane, aminoethylaminopropylmethyldimethoxysilane, aminoethylaminopropylmethyldiethoxysilane, aminoethylaminomethyltriethoxysilane, aminoethylaminomethylmethyldiethoxysilane, diethylenetriaminopropyltrimethoxysilane, diethylenetriaminopropyltriethoxysilane, diethylenetriaminopropylmethyldimethoxysilane, diethyleneaminomethylmethyldiethoxysilane, (N-phenylamino)methyltrimethoxysilane, (N-phenylamino)methyltriethoxysilane, (N-phenylamino)methylmethyldimethoxysilane, (N-phenylamino)methylmethyldiethoxysilane, 3-(N-phenylamino)propyltrimethoxysilane, 3-(N-phenylamino)propyltriethoxysilane, 3-(N-phenylamino)propylmethyldimethoxysilane, 3-(N-phenylamino)propylmethyldiethoxysilane, and N—(N-butyl)-3-aminopropyltrimethoxysilane. The amino silane compound may be used alone or as a mixture type.

The amounts of the unsaturated silane compound and/or the amino silane compound are not specifically limited.

In addition, the composition for an encapsulant film may additionally include one or more additives selected from a light stabilizer, a UV absorbent and a thermal stabilizer as necessary.

The light stabilizer may capture the active species of the photothermal initiation of a resin to prevent photooxidation according to the use applied of the composition. The type of the light stabilizer used is not specifically limited, and for example, known compounds such as a hindered amine-based compound and a hindered piperidine-based compound may be used.

The UV absorbent absorbs ultraviolet rays from the sunlight, etc. and transform into harmless thermal energy in a molecule, and may play the role of preventing the excitation of the active species of photothermal initiation in the resin composition. Particular types of the UV absorbent used are not specifically limited, and for example, one or a mixture of two or more of benzophenone-based, benzotriazole-based, acrylnitrile-based, metal complex-based, hindered amine-based, inorganic including ultrafine particulate titanium oxide and ultrafine particulate zinc oxide UV absorbents, etc. may be used.

In addition, the thermal stabilizer may include a phosphor-based thermal stabilizer such as tris(2,4-di-tert-butylphenyl)phosphite, phosphorous acid, bis[2,4-bis(1,1-dimethylethyl)-6-methylphenyl]ethylester, tetrakis(2,4-di-tert-butylphenyl)[1,1-biphenyl]-4,4′-diylbisphosphonate and bis(2,4-di-tert-butylphenyl)pentaerythritol diphosphite; and a lactone-based thermal stabilizer such as the reaction product of 8-hydroxy-5,7-di-tert-butyl-furan-2-on and o-xylene, and one or two or more of them may be used.

The amounts of the light stabilizer, UV absorbent and/or thermal stabilizer are not specifically limited. That is, the amounts of the additives may be suitably selected considering the use of the resin composition, the shape or density of the additives, etc. Generally, the amounts may be suitably controlled in a range of 0.01 to 5 parts by weight based on 100 parts by weight of the total solid content of the composition for an encapsulant film.

In addition, the composition for an encapsulant film of the present invention may additionally include various additives well-known in this art according to the use of the resin component applied in addition to the above components.

In addition, the composition for an encapsulant film may be utilized in various molded articles by molding by injection, extrusion, etc. Particularly, the composition may be used in various optoelectronic devices, for example, as an encapsulant for the encapsulation of a device in a solar cell, and may be used as an industrial material applied in a lamination process with heating, etc., without limitation.

[Method for Preparing Ethylene/Alpha-Olefin Copolymer]

The method for preparing a composition for an encapsulant film of the present invention is characterized in including: a step of polymerizing ethylene and an alpha-olefin-based monomer in the presence of a catalyst composition including transition metal compounds represented by Formula 1 and Formula 2 below to prepare an ethylene/alpha-olefin copolymer; and a step of mixing the ethylene/alpha-olefin copolymer with a crosslinking agent, a crosslinking auxiliary agent and a silane coupling agent.

In Formula 1,

R₁ is hydrogen; alkyl of 1 to 20 carbon atoms; cycloalkyl of 3 to 20 carbon atoms; alkenyl of 2 to 20 carbon atoms; alkoxy of 1 to 20 carbon atoms; aryl of 6 to 20 carbon atoms; arylalkoxy of 7 to 20 carbon atoms; alkylaryl of 7 to 20 carbon atoms; or arylalkyl of 7 to 20 carbon atoms,

R₂ and R₃ are each independently hydrogen; halogen; alkyl of 1 to 20 carbon atoms; cycloalkyl of 3 to 20 carbon atoms; alkenyl of 2 to 20 carbon atoms; arylalkyl of 7 to 20 carbon atoms; alkylamido of 1 to 20 carbon atoms; or arylamido of 6 to 20 carbon atoms,

R₄ and R₅ are each independently hydrogen; alkyl of 1 to 20 carbon atoms; cycloalkyl of 3 to 20 carbon atoms; aryl of 6 to 20 carbon atoms; or alkenyl of 2 to 20 carbon atoms,

R₆ to R₉ are each independently hydrogen; alkyl of 1 to 20 carbon atoms; cycloalkyl of 3 to 20 carbon atoms; aryl of 6 to 20 carbon atoms; or alkenyl of 2 to 20 carbon atoms,

two or more adjacent groups among R₂ to R₉ may be connected with each other to form a ring,

Q₁ is Si, C, N, P or S,

M₁ is Ti, Hf or Zr, and

X₁ and X₂ are each independently hydrogen; halogen; alkyl of 1 to 20 carbon atoms; alkenyl of 2 to 20 carbon atoms; aryl of 6 to 20 carbon atoms; alkylaryl of 7 to 20 carbon atoms; arylalkyl of 7 to 20 carbon atoms; alkylamino of 1 to 20 carbon atoms; or arylamino of 6 to 20 carbon atoms.

In Formula 2,

R₁₀ is hydrogen; alkyl of 1 to 20 carbon atoms; cycloalkyl of 3 to 20 carbon atoms; alkenyl of 2 to 20 carbon atoms; alkoxy of 1 to 20 carbon atoms; aryl of 6 to 20 carbon atoms; arylalkoxy of 7 to 20 carbon atoms; alkylaryl of 7 to 20 carbon atoms; or arylalkyl of 7 to 20 carbon atoms,

R_(11a) to R_(11e) are each independently hydrogen; halogen; alkyl of 1 to 20 carbon atoms; cycloalkyl of 3 to 20 carbon atoms; alkenyl of 2 to 20 carbon atoms; alkoxy of 1 to 20 carbon atoms; or aryl of 6 to 20 carbon atoms,

R₁₂ is hydrogen; halogen; alkyl of 1 to 20 carbon atoms; cycloalkyl of 3 to 20 carbon atoms; alkenyl of 2 to 20 carbon atoms; aryl of 6 to 20 carbon atoms; alkylaryl of 7 to 20 carbon atoms; arylalkyl of 7 to 20 carbon atoms; alkylamido of 1 to 20 carbon atoms; or arylamido of 6 to 20 carbon atoms,

R₁₃ and R₁₄ are each independently hydrogen; alkyl of 1 to 20 carbon atoms; cycloalkyl of 3 to 20 carbon atoms; aryl of 6 to 20 carbon atoms; or alkenyl of 2 to 20 carbon atoms,

R₁₅ to R₁₈ are each independently hydrogen; alkyl of 1 to 20 carbon atoms; cycloalkyl of 3 to 20 carbon atoms; aryl of 6 to 20 carbon atoms; or alkenyl of 2 to 20 carbon atoms,

two or more adjacent groups among R₁₅ to R₁₈ may be connected with each other to form a ring,

Q₂ is Si, C, N, P or S,

M₂ is Ti, Hf or Zr, and

X₃ and X₄ are each independently hydrogen; halogen; alkyl of 1 to 20 carbon atoms; alkenyl of 2 to 20 carbon atoms; aryl of 6 to 20 carbon atoms; alkylaryl of 7 to 20 carbon atoms; arylalkyl of 7 to 20 carbon atoms; alkylamino of 1 to 20 carbon atoms; or arylamino of 6 to 20 carbon atoms.

Particularly, in Formula 1, R₁ is hydrogen; alkyl of 1 to 20 carbon atoms; cycloalkyl of 3 to 20 carbon atoms; alkenyl of 2 to 20 carbon atoms; alkoxy of 1 to 20 carbon atoms; aryl of 6 to 20 carbon atoms; arylalkoxy of 7 to 20 carbon atoms; alkylaryl of 7 to 20 carbon atoms; or arylalkyl of 7 to 20 carbon atoms, and more particularly, R₁ may be methyl, ethyl, propyl, butyl, isobutyl, tert-butyl, isopropyl, cyclohexyl, benzyl, phenyl, methoxyphenyl, ethoxyphenyl, fluorophenyl, bromophenyl, chlorophenyl, dimethylphenyl or diethylphenyl.

Particularly, in Formula 1, R₂ and R₃ are each independently hydrogen; halogen; alkyl of 1 to 20 carbon atoms; cycloalkyl of 3 to 20 carbon atoms; alkenyl of 2 to 20 carbon atoms; arylalkyl of 7 to 20 carbon atoms; alkylamido of 1 to 20 carbon atoms; or arylamido of 6 to 20 carbon atoms, and more particularly, R₂ and R₃ may be each independently hydrogen; alkyl of 1 to 20 carbon atoms; or arylalkyl of 7 to 20 carbon atoms.

Particularly, in Formula 1, R₄ and R₅ may be the same or different, and may be each independently hydrogen; alkyl of 1 to 20 carbon atoms; cycloalkyl of 3 to 20 carbon atoms; aryl of 6 to 20 carbon atoms; or alkenyl of 2 to 20 carbon atoms, more particularly, alkyl of 1 to 6 carbon atoms. More particularly, R₄ and R₅ may be methyl, ethyl or propyl.

Particularly, in Formula 1, R₆ to R₉ may be the same or different and may be each independently hydrogen; alkyl of 1 to 20 carbon atoms; cycloalkyl of 3 to 20 carbon atoms; aryl of 6 to 20 carbon atoms; or alkenyl of 2 to 20 carbon atoms. More particularly, R₆ to R₉ may be the same or different and may be each independently hydrogen or methyl.

Two or more adjacent groups among R₆ to R₉ may be connected with each other to form an aliphatic ring of 5 to 20 carbon atoms or an aromatic ring of 6 to 20 carbon atoms, and the aliphatic ring or aromatic ring may be substituted with halogen, alkyl of 1 to 20 carbon atoms, alkenyl of 2 to 20 carbon atoms or aryl of 6 to 20 carbon atoms.

Particularly, in Formula 1, Q₁ is Si, C, N, P or S, and more particularly, Q₁ may be Si.

Particularly, in Formula 1, M₁ may be Ti, Hf or Zr.

Particularly, in Formula 1, X₁ and X₂ may be the same or different and may be each independently hydrogen; halogen; alkyl of 1 to 20 carbon atoms; alkenyl of 2 to 20 carbon atoms; aryl of 6 to 20 carbon atoms; alkylaryl of 7 to 20 carbon atoms; arylalkyl of 7 to 20 carbon atoms; alkylamino of 1 to 20 carbon atoms; or arylamino of 6 to 20 carbon atoms.

In addition, the compound represented by Formula 1 may be a compound represented by any one among the compounds below.

Besides, the compounds may have various structures within the range defined in Formula 1.

In addition, in Formula 2, R₁₀ is hydrogen; alkyl of 1 to 20 carbon atoms; cycloalkyl of 3 to 20 carbon atoms; alkenyl of 2 to 20 carbon atoms; alkoxy of 1 to 20 carbon atoms; aryl of 6 to 20 carbon atoms; arylalkoxy of 7 to 20 carbon atoms; alkylaryl of 7 to 20 carbon atoms; or arylalkyl of 7 to 20 carbon atoms, and more particularly, R₁₀ may be hydrogen; alkyl of 1 to 20 carbon atoms or 1 to 12 carbon atoms; alkoxy of 1 to 20 carbon atoms; aryl of 6 to 20 carbon atoms; arylalkoxy of 7 to 20 carbon atoms; alkylaryl of 7 to 20 carbon atoms; or arylalkyl of 7 to 20 carbon atoms.

Particularly, in Formula 2, R_(11a) to R_(11e) are each independently hydrogen; halogen; alkyl of 1 to 20 carbon atoms; cycloalkyl of 3 to 20 carbon atoms; alkenyl of 2 to 20 carbon atoms; alkoxy of 1 to 20 carbon atoms; or aryl of 6 to 20 carbon atoms, more particularly, hydrogen; halogen; alkyl of 1 to 12 carbon atoms; cycloalkyl of 3 to 12 carbon atoms; alkenyl of 2 to 12 carbon atoms; alkoxy of 1 to 12 carbon atoms; or phenyl.

Particularly, in Formula 2, R₁₂ is hydrogen; halogen; alkyl of 1 to 20 carbon atoms; cycloalkyl of 3 to 20 carbon atoms; alkenyl of 2 to 20 carbon atoms; aryl of 6 to 20 carbon atoms; alkylaryl of 7 to 20 carbon atoms; arylalkyl of 7 to 20 carbon atoms; alkylamido of 1 to 20 carbon atoms; or arylamido of 6 to 20 carbon atoms, more particularly, hydrogen; halogen; alkyl of 1 to 12 carbon atoms; cycloalkyl of 3 to 12 carbon atoms; alkenyl of 2 to 12 carbon atoms; or phenyl.

Particularly, in Formula 2, R₁₃ and R₁₄ are each independently hydrogen; alkyl of 1 to 20 carbon atoms; cycloalkyl of 3 to 20 carbon atoms; aryl of 6 to 20 carbon atoms; or alkenyl of 2 to 20 carbon atoms, more particularly, hydrogen; or alkyl of 1 to 12 carbon atoms.

Particularly, in Formula 2, R₁₅ to R₁₈ are each independently hydrogen; alkyl of 1 to 20 carbon atoms; cycloalkyl of 3 to 20 carbon atoms; aryl of 6 to 20 carbon atoms; or alkenyl of 2 to 20 carbon atoms, more particularly, hydrogen; alkyl of 1 to 12 carbon atoms; or cycloalkyl of 3 to 12 carbon atoms, or hydrogen; or methyl.

Particularly, in Formula 2, two or more adjacent groups among R₁₅ to R₁₈ may be connected with each other to form a ring.

Particularly, in Formula 2, Q₂ is Si, C, N, P or S, more particularly, Q may be Si.

Particularly, in Formula 2, X₃ and X₄ are each independently hydrogen; halogen; alkyl of 1 to 20 carbon atoms; alkenyl of 2 to 20 carbon atoms; aryl of 6 to 20 carbon atoms; alkylaryl of 7 to 20 carbon atoms; arylalkyl of 7 to 20 carbon atoms; alkylamino of 1 to 20 carbon atoms; or arylamino of 6 to 20 carbon atoms, particularly, hydrogen; halogen; alkyl of 1 to 12 carbon atoms; cycloalkyl of 3 to 12 carbon atoms; or alkenyl of 2 to 12 carbon atoms, more particularly, hydrogen; or alkyl of 1 to 12 carbon atoms.

In addition, the compound represented by Formula 2 may be any one among the compounds represented by Formula 2-1 to Formula 2-10 below.

In the present invention, the molar ratio of the transition metal compounds represented by Formula 1 and Formula 2 may be 1:1.2 to 1:10, or 1:1.5 to 1:9, 1:2 to 1:5, or 1:2 to 1:4, without limitation.

As described above, the transition metal compounds represented by Formula 1 and Formula 2 used in the present invention have different mixing and introducing capacity of a comonomer, and by mixing and using them, a copolymer having both a low-density region and a high-density region and high crystallinity distribution may be prepared, and the copolymer of the present invention thus prepared may show high crystallinity distribution, a small free volume, and excellent electrical insulation.

In the present invention, the polymerization reaction may be performed by continuously polymerizing ethylene and an alpha-olefin-based monomer by continuously injecting hydrogen in the presence of the catalyst composition, particularly, may be performed by injecting hydrogen in 5 to 100 cc/min.

The hydrogen gas plays the role of restraining vigorous reaction of the transition metal compounds at the initiation point of polymerization and terminating polymerization reaction. Accordingly, by the use of the hydrogen gas and the control of the amount used, an ethylene/alpha-olefin copolymer having narrow molecular weight distribution may be effectively prepared.

For example, the hydrogen may be injected in 5 cc/min or more, 7 cc/min or more, or 10 cc/min or more, or 15 cc/min or more, or 19 cc/min or more, and 100 cc/min or less, or 50 cc/min or less, or 45 cc/min or less, or 35 cc/min or less, or 29 cc/min or less. If injected in the above-described conditions, the ethylene/alpha-olefin copolymer thus prepared may achieve the physical properties of the present invention.

If the hydrogen gas is injected in less than 5 cc/min, the termination of polymerization reaction is not uniformly carried out, and the preparation of an ethylene/alpha-olefin copolymer having desired physical properties may become difficult, and if injected in greater than 100 cc/min, termination reaction may occur too fast, and it is apprehended that an ethylene/alpha-olefin copolymer having a very low molecular weight may be prepared.

In addition, the polymerization reaction may be performed at 100 to 200° C., and by controlling the polymerization temperature together with the injection amount of hydrogen, the crystallinity distribution and the molecular weight distribution in the ethylene/alpha-olefin copolymer may be controlled more advantageously. Particularly, the polymerization reaction may be performed at 100 to 200° C., 120 to 180° C., 130 to 170° C., or 140 to 160° C., without limitation.

In the present invention, a co-catalyst may be additionally used in the catalyst composition for activating the transition metal compounds represented by Formula 1 and/or Formula 2. The co-catalyst is an organometallic compound including a metal in group 13, and may particularly include one or more selected from Formula 3 to Formula 5 below.

—[Al(R₁₉)—O]_(a)—  [Formula 3]

In Formula 3,

each R₁₉ is independently halogen radical;

hydrocarbyl radical of 1 to 20 carbon atoms; or halogen-substituted hydrocarbyl radical of 1 to 20 carbon atoms, and

a is an integer of 2 or more.

D(R₁₉)₃  [Formula 4]

In Formula 4,

D is aluminum or boron, and

each R₁₉ is independently halogen radical; hydrocarbyl radical of 1 to 20 carbon atoms; or halogen-substituted hydrocarbyl radical of 1 to 20 carbon atoms.

[L-H]⁺[Z(A)₄]⁻ or [L]⁺[Z(A)₄]⁻  [Formula 5]

In Formula 5,

H is a hydrogen atom,

Z is an element in group 13,

each A is independently aryl of 6 to 20 carbon atoms, in which one or more hydrogen atoms may be substituted as substituents; or alkyl of 1 to 20 carbon atoms,

the substituent is halogen; hydrocarbyl of 1 to 20 carbon atoms; alkoxy of 1 to 20 carbon atoms; or aryloxy of 6 to 20 carbon atoms,

[L-H]⁺ is trimethylammonium; triethylammonium;

tripropylammonium; tributylammonium; diethylammonium;

trimethylphosphonium; or triphenylphosphonium, and

[L]⁺ is N,N-diethylanilinium; or triphenylcarbonium.

More particularly, the compound of Formula 3 may be an alkylaluminoxane-based compound in which repeating units are combined in a linear, circular or network shape, and particular example may include methylaluminoxane (MAO), ethylaluminoxane, isobutylaluminoxane or tert-butylaluminoxane.

In addition, the compound of Formula 4 may include trimethylaluminum, triethylaluminum, triisobutylaluminum, tripropylaluminum, tributylaluminum, dimethylchloroaluminum, triisopropylaluminum, tri-s-butylaluminum, tricyclopentylaluminum, tripentylaluminum, triisopentylaluminum, trihexylaluminum, trioctylaluminum, ethyldimethylaluminum, methyldiethylaluminum, triphenylaluminum, tri-p-tolylaluminum, dimethylaluminummethoxide, dimethylaluminumethoxide, trimethylboron, triethylboron, triisobutylboron, tripropylboron, tributylboron, etc., particularly, trimethylaluminum, triethylaluminum or triisobutylaluminum, without limitation.

In addition, the compound of Formula 5 may include a borate-based compound of a trisubstituted ammonium salt, a dialkyl ammonium salt or a trisubstituted phosphonium salt type. More particular examples include a borate-based compound of a trisubstituted ammonium salt type such as trimethylammonium tetraphenylborate, methyldioctadecylammonium tetraphenylborate, triethylammonium tetraphenylborate, tripropylammonium tetraphenylborate, tri(n-butyl)ammonium tetraphenylborate, methyltetradecylcyclooctadecylammonium tetraphenylborate, N,N-dimethylanilinium tetraphenylborate, N,N-diethylanilinium tetraphenylborate, N,N-dimethyl(2,4,6-trimethylanilinium)tetraphenylborate, trimethylammonium tetrakis(pentafluorophenyl)borate, methylditetradecylammonium tetrakis(pentaphenyl)borate, methyldioctadecylammonium tetrakis(pentafluorophenyl)borate, triethylammonium, tetrakis(pentafluorophenyl)borate, tripropylammoniumtetrakis(pentafluorophenyl)borate, tri(n-butyl)ammonium tetrakis(pentafluorophenyl)borate, tri(sec-butyl)ammoniumtetrakis(pentafluorophenyl)borate, N,N-dimethylanilinium tetrakis(pentafluorophenyl)borate, N,N-diethylaniliniumtetrakis(pentafluorophenyl)borate, N,N-dimethyl(2,4,6-trimethylanilinium)tetrakis(pentafluorophenyl)borate, trimethylammoniumtetrakis(2,3,4,6-tetrafluorophenyl)borate, triethylammonium tetrakis(2,3,4,6-tetrafluorophenyl)borate, tripropylammonium tetrakis(2,3,4,6-tetrafluorophenyl)borate, tri(n-butyl)ammonium tetrakis(2,3,4,6-,tetrafluorophenyl)borate, dimethyl(t-butyl)ammonium tetrakis(2,3,4,6-tetrafluorophenyl)borate, N,N-dimethylanilinium tetrakis(2,3,4,6-tetrafluorophenyl)borate, N,N-diethylanilinium tetrakis(2,3,4,6-tetrafluorophenyl)borate and N,N-dimethyl-(2,4,6-trimethylanilinium)tetrakis-(2,3,4,6-tetrafluorophenyl)borate; a borate-based compound of a dialkyl ammonium salt type such as dioctadecylammonium tetrakis(pentafluorophenyl)borate, ditetradecylammonium tetrakis(pentafluorophenyl)borate and dicyclohexylammonium tetrakis(pentafluorophenyl)borate; or a borate-based compound of a trisubstituted phosphonium salt type such as triphenylphosphonium tetrakis(pentafluorophenyl)borate, methyldioctadecylphosphonium tetrakis(pentafluorophenyl)borate and tri(2,6-, dimethylphenyl)phosphoniumtetrakis(pentafluorophenyl)borate, without limitation.

By using such a co-catalyst, the molecular weight distribution of the ethylene/alpha-olefin copolymer finally prepared may become more uniform, and polymerization activity may be improved.

The co-catalyst may be used in a suitable amount so that the activation of the transition metal compounds of Formula 1 and/or Formula 2 may be sufficiently achieved.

In the present invention, the transition metal compounds of Formula 1 and/or Formula 2 may be used in a supported type on a support.

In case where the transition metal compounds of Formula 1 and/or Formula 2 are supported by the support, the weight ratio of the transition metals and the support may be 1:10 to 1:1,000, more particularly, 1:10 to 1:500. If the support and the transition metal compounds are included in a weight ratio in the above range, optimized type may be shown. In addition, if the co-catalyst is supported together by the support, the weight ratio of the co-catalyst and the support may be 1:1 to 1:100, more particularly, 1:1 to 1:50. If the co-catalyst and the support are included in the weight ratio, catalyst activity may be improved, and the microstructure of a polymer prepared may be optimized.

Meanwhile, silica, alumina, magnesia or mixtures thereof may be used as the support, or these materials may be used after drying at a high temperature to remove moisture at the surface and in a state including a hydroxyl group or siloxane group which has high reactivity at the surface. Also, the dried support at a high temperature may further include an oxide, a carbonate, a sulfate or a nitrate component such as Na₂O, K₂CO₃, BaSO₄ and Mg(NO₃)₂.

The drying temperature of the support is preferably, from 200 to 800° C., more preferably, from 300 to 600° C., most preferably, from 300 to 400° C. If the drying temperature of the support is less than 200° C., humidity is too high and moisture at the surface may react with the co-catalyst, and if the temperature is greater than 800° C., the pores at the surface of the support may be combined to decrease the surface area, and a large amount of the hydroxyl groups at the surface may be removed to remain only siloxane groups to decrease reaction sites with the co-catalyst, undesirably.

In addition, the amount of the hydroxyl group at the surface of the support may preferably be 0.1 to 10 mmol/g, more preferably, 0.5 to 5 mmol/g. The amount of the hydroxyl group at the surface of the support may be controlled by the preparation method and conditions of the support, or drying conditions, for example, temperature, time, vacuum or spray drying.

In addition, an organoaluminum compound may be further injected for removing moisture in a reactor during polymerization reaction, and the polymerization reaction may be performed in the presence thereof. Particular examples of such organoaluminum compound may include trialkylaluminum, dialkylaluminum halide, alkyl aluminum dihalide, aluminum dialkyl hydride or alkyl aluminum sesqui halide, and more particular examples may include Al(C₂H₅)₃, Al(C₂H₅)₂H, Al(C₃H₇)₃, Al(C₃H₇)₂H, Al(i-C₄H₉)₂H, Al(C₈H₁₇)₃, Al(C₁₂H₂₅)₃, Al(C₂H₅)(C₁₂H₂₅)₂, Al(i-C₄H₉)(C₁₂H₂₅)₂, Al(i-C₄H₉)₂H, Al(i-C₄H₉)₃, (C₂H₅)₂AlCl, (i-C₃H₉)₂AlCl, (C₂H₅)₃Al₂Cl₃, etc. Such organoaluminum compound may be continuously injected into a reactor, or may be injected in a ratio of about 0.1 to 10 mol per 1 kg of a reaction medium injected into the reactor for suitable removal of moisture.

In addition, a polymerization pressure may be about 1 to about 100 Kgf/cm², preferably, about 1 to about 50 Kgf/cm², more preferably, about 5 to about 30 Kgf/cm².

Also, if the transition metal compound is used in a supported type by a support, the transition metal compound may be injected after being dissolved or diluted in an aliphatic hydrocarbon solvent of 5 to 12 carbon atoms, for example, pentane, hexane, heptane, nonane, decane, and isomers thereof, an aromatic hydrocarbon solvent such as toluene and benzene, or a hydrocarbon solvent substituted with a chlorine atom such as dichloromethane and chlorobenzene. The solvent used is preferably used after treating with a small amount of alkyl aluminum to remove a small amount of water or air, which acts as a catalyst poison, and may be used by using a co-catalyst further.

[Encapsulant Film and Solar Cell Module]

In addition, the composition for an encapsulant film of the present invention may be included in an encapsulant film and used.

The encapsulant film of the present invention may be prepared by molding the composition for an encapsulant film into a film or sheet shape. The molding method is not specifically limited, for example, a sheet or a film may be formed by a common process such as a T die process and extrusion. For example, the manufacture of the encapsulant film may be performed in situ using an apparatus in which the preparation of a modified resin composition using the composition for an encapsulant film and a process for forming a film or a sheet are connected.

The thickness of the encapsulant film may be controlled to about 10 to 2,000 μm, or about 100 to 1,250 μm considering the supporting efficiency and breaking possibility of a device in an optoelectronic device, the reduction of the weight or workability of the device, and may be changed according to the particular use thereof.

In addition, the present invention provides a solar cell module including the encapsulant film. In the present invention, the solar cell module may have a configuration in which the gaps between the solar cells disposed in series or in parallel are filled with the encapsulant film of the present invention, a glass surface is disposed on a side where the sunlight strikes, and a backside is protected by a back sheet, but is not limited thereto. Various types and shapes of the solar cell modules manufactured by including the encapsulant film in this technical field may be applied in the present invention.

The glass surface may use tempered glass for protecting the solar cells from external impact and preventing breaking, and may use low iron tempered glass having low iron content to prevent the reflection of the sunlight and to increase the transmittance of the sunlight, without limitation.

The back sheet is a climate-resistant film protecting the backside of the solar cell module from exterior, for example, a fluorine-based resin sheet, a metal plate or metal film such as aluminum, a cyclic olefin-based resin sheet, a polycarbonate-based resin sheet, a poly(meth)acryl-based resin sheet, a polyamide-based resin sheet, a polyester-based resin sheet, a laminated composite sheet of a climate-resistant film and a barrier film, etc., without limitation.

Besides, the solar cell module of the present invention may be manufactured by any methods well-known in this technical field only if including the encapsulant film, without limitation.

The solar cell module of the present invention is manufactured using an encapsulant film having excellent volume resistance, and the leakage of current outside through the movement of electrons in the solar cell module may be prevented through the encapsulant film. Accordingly, potential induced degradation phenomenon (PID) by which insulation is degraded, leakage current is generated, and the output of the module is rapidly degraded, may be largely restrained.

EXAMPLES

Hereinafter, the present invention will be explained in more detail referring to embodiments. However, the embodiments are provided only for illustration of the present invention, and the scope of the present invention is not limited thereto.

Preparation of Transition Metal Compound Synthetic Example 1 (1) Preparation of Ligand Compound Synthesis of N-tert-butyl-1-(1,2-dimethyl-3H-benzo[b]cyclopenta[d]thiophen-3-yl)-1,1-dimethylsilanamine

To a 100 ml schlenk flask, 4.65 g (15.88 mmol) of the compound of Formula 3 was weighed and added, and 80 ml of THF was injected thereto. At room temperature, tBuNH₂ (4 eq, 6.68 ml) was injected thereto and reacted at room temperature for 3 days. After finishing the reaction, THF was removed, and the resultant reaction product was filtered with hexane. After drying solvents, 4.50 g (86%) of a yellow liquid was obtained.

¹H-NMR (in CDCl₃, 500 MHz): 7.99 (d, 1H), 7.83 (d, 1H), 7.35 (dd, 1H), 7.24 (dd, 1H), 3.49 (s, 1H), 2.37 (s, 3H), 2.17 (s, 3H), 1.27 (s, 9H), 0.19 (s, 3H), −0.17 (s, 3H).

(2) Preparation of Transition Metal Compound

To a 50 ml schlenk flask, the ligand compound (1.06 g, 3.22 mmol/1.0 eq) and 16.0 ml (0.2 M) of MTBE were put and stirred first. n-BuLi (2.64 ml, 6.60 mmol/2.05 eq, 2.5 M in THF) was added thereto at −40° C. and reacted at room temperature overnight. After that, MeMgBr (2.68 ml, 8.05 mmol/2.5 eq, 3.0 M in diethyl ether) was slowly added thereto dropwisely at −40° C., and TiCl₄ (2.68 ml, 3.22 mmol/1.0 eq, 1.0 M in toluene) was put in order, followed by reacting at room temperature overnight. After that, the reaction mixture was passed through celite using hexane for filtration. After dying the solvents, 1.07 g (82%) of a brown solid was obtained.

¹H-NMR (in CDCl₃, 500 MHz): 7.99 (d, 1H), 7.68 (d, 1H), 7.40 (dd, 1H), 7.30 (dd, 1H), 3.22 (s, 1H), 2.67 (s, 3H), 2.05 (s, 3H), 1.54 (s, 9H), 0.58 (s, 3H), 0.57 (s, 3H), 0.40 (s, 3H), −0.45 (s, 3H).

Synthetic Example 2 (1) Preparation of Ligand Compound Synthesis of N-tert-butyl-1-(1,2-dimethyl-3H-benzo[b]cyclopenta[d]thiophene-3-yl)-1,1-(2-ethylphenyl)(methyl)silanamine (i) Preparation of chloro-1-(1,2-dimethyl-3H-benzo[b]cyclopenta[d]thiophene-3-yl)-1,1-(2-ethylphenyl)(methyl)silane

To a 100 ml schlenk flask, 2 g (1 eq, 9.99 mmol) of 1,2-dimethyl-3H-benzo[b]cyclopenta[d]thiophene and 50 ml of THF were put, and 4 ml (1 eq, 9.99 mmol, 2.5 M in hexane) of n-BuLi was added thereto dropwisely at −30° C., followed by stirring at room temperature overnight. A stirred Li-complex THF solution was cannulated into a schlenk flask containing 2.19 ml (1.0 eq, 9.99 mmol) of dichloro(2-ethylphenyl)(methyl)silane and 50 ml of THF at −78° C., followed by stirring at room temperature overnight. After stirring, drying in vacuum was carried out and extraction with 60 ml of hexane was carried out. After drying again in vacuum and washing with hexane, 3.83 g (99%, dr=1:1) of an ivory solid was obtained.

(ii) Preparation of N-tert-butyl-1-(1,2-dimethyl-3H-benzo[b]cyclopenta[d]thiophene-3-yl)-1,1-(2-ethylphenyl)(methyl)silanamine

To 100 ml round flask, 3.87 g (10.1 mmol) of chloro-1-(1,2-dimethyl-3H-benzo[b]cyclopenta[d]thiophene-3-yl)-1,1-(2-ethylphenyl)(methyl)silane was weighed and added, and 40 ml of hexane was injected thereto. At room temperature, t-BuNH₂ (10 eq, 10.5 mL) was injected and reacted at room temperature for 2 days. After the reaction, hexane was removed, and filtering with hexane was carried out. After drying the solvents, 3.58 g (84.4%, dr=1:0.8) of a yellow solid was obtained.

¹H-NMR (CDCl₃, 500 MHz): δ 7.98 (t, 2H), 7.71 (d, 1H), 7.55 (d, 1H), 7.52 (d, 1H), 7.48 (d, 1H), 7.30 (t, 1H), 7.26-7.22 (m, 3H), 7.19 (dd, 2H), 7.12-7.06 (m, 3H), 7.00 (t, 1H), 3.08-2.84 (m, 4H) 3.05-2.84 (m, 2H), 2.28 (s, 3H), 2.20 (s, 3H), 2.08 (s, 3H), 1.62 (s, 3H), 1.26-1.22 (m, 6H), 1.06 (s, 9H), 0.99 (s, 9H), 0.05 (s, 3H), −0.02 (s, 3H).

(2) Preparation of Transition Metal Compound

To a 50 ml vial, the ligand compound (1.74 g, 4.14 mmol/1.0 eq) and 20.7 ml (0.2 M) of toluene were put and stirred. n-BuLi (3.48 ml, 8.7 mmol/2.1 eq, 2.5 M in hexane) was added thereto at −40° C. and stirred at room temperature overnight. Then, MeMgBr (4.14 ml, 12.42 mmol/3.0 eq, 3.0 M in diethyl ether) was slowly added thereto dropwisely at −40° C., and TiCl₄DME (1.1 g, 4.14 mmol/1.0 eq) was put in order, followed by stirring at room temperature overnight. After drying the solvents, the reaction mixture was filtered using hexane. Then, DME (1.29 ml, 12.42 mmol/3 eq) was added to the filtrate and stirred at room temperature overnight. After drying the solvents, the resultant product was filtered using hexane to obtain 335 mg (16.3%, dr=1:0.8) of a yellow solid.

¹H NMR (CDCl₃, 500 MHz): δ 7.90 (d, 1H), 7.85 (d, 1H), 7.74 (d, 1H), 7.71 (d, 1H), 7.40 (d, 1H), 7.37 (d, 1H), 7.27 (d, 1H), 7.23 (t, 2H), 7.17 (t, 2H), 7.13 (t, 2H), 7.06 (t, 1H), 7.01 (t, 1H), 6.86 (t, 1H), 2.97-2.91 (m, 2H), 2.90-2.82 (m, 2H), 2.33 (s, 3H), 2.22 (s, 3H), 1.96 (s, 3H), 1.68 (s, 9H), 1.66 (s, 9H), 1.38 (s, 3H), 1.32 (t, 3H), 1.24 (t, 3H), 1.07 (s, 3H), 0.88 (s, 3H), 0.85 (s, 3H), 0.72 (s, 3H), 0.19 (s, 3H), 0.01 (s, 3H).

Synthetic Example 3 (1) Preparation of Ligand Compound Synthesis of N-tert-butyl-1-(1,2-dimethyl-3H-benzo[b]cyclopenta[d]thiophene-3-yl)-1,1-(methyl)(phenyl)silanamine (i) Preparation of chloro-1-(1,2-dimethyl-3H-benzo[b]cyclopenta[d]thiophene-3-yl)-1,1-(methyl)(phenyl)silane

To a 250 ml schlenk flask, 10 g (1.0 eq, 49.925 mmol) of 1,2-dimethyl-3H-benzo[b]cyclopenta[d]thiophene and 100 ml of THF were put, and 22 ml (1.1 eq, 54.918 mmol, 2.5 M in hexane) of n-BuLi was added thereto dropwisely at −30° C., followed by stirring at room temperature for 3 hours. A stirred Li-complex THF solution was cannulated into a schlenk flask containing 8.1 ml (1.0 eq, 49.925 mmol) of dichloro(methyl)(phenyl)silane and 70 ml of THF at −78° C., followed by stirring at room temperature overnight. After stirring, drying in vacuum was carried out, and extraction with 100 ml of hexane was carried out.

(ii) Preparation of N-tert-butyl-1-(1,2-dimethyl-3H-benzo[b]cyclopenta[d]thiophene-3-yl)-1,1-(methyl)(phenyl)silanamine

After injecting 42 ml (8 eq, 399.4 mmol) of t-BuNH₂ to 100 ml of the extracted chloro-1-(1,2-dimethyl-3H-benzo[b]cyclopenta[d]thiophene-3-yl)-1,1-(methyl)(phenyl)silane hexane solution at room temperature, stirring was performed at room temperature overnight. After stirring, drying in vacuum was carried out, and extraction with 150 ml of hexane was carried out. After drying the solvents, 13.36 g (68%, dr=1:1) of a yellow solid was obtained.

¹H NMR (CDCl₃, 500 MHz): δ 7.93 (t, 2H), 7.79 (d, 1H), 7.71 (d, 1H), 7.60 (d, 2H), 7.48 (d, 2H), 7.40˜7.10 (m, 10H, aromatic), 3.62 (s, 1H), 3.60 (s, 1H), 2.28 (s, 6H), 2.09 (s, 3H), 1.76 (s, 3H), 1.12 (s, 18H), 0.23 (s, 3H), 0.13 (s, 3H).

(2) Preparation of Transition Metal Compound

To a 100 ml schlenk flask, 4.93 g (12.575 mmol, 1.0 eq) of the ligand compound of Formula 2-4 and 50 ml (0.2 M) of toluene were put, and 10.3 ml (22.779 mmol, 2.05 eq, 2.5 M in hexane) of n-BuLi was added thereto dropwisely at −30° C., followed by stirring at room temperature overnight. After stirring, 12.6 ml (37.725 mmol, 3.0 eq, 3.0 M in diethyl ether) of MeMgBr was added thereto dropwisely, and 13.2 ml (13.204 mmol, 1.05 eq, 1.0 M in toluene) of TiCl₄ was put in order, followed by stirring at room temperature overnight.

After stirring, the reaction product was dried in vacuum and extracted with 150 ml of hexane. The solvents were removed to 50 ml, and 4 ml (37.725 mmol, 3.0 eq) of DME was added dropwisely and stirred at room temperature overnight. After drying again in vacuum and extracting with 150 ml of hexane, 2.23 g (38%, dr=1:0.5) of a brown solid was obtained.

¹H NMR (CDCl₃, 500 MHz): δ 7.98 (d, 1H), 7.94 (d, 1H), 7.71 (t, 6H), 7.50˜7.30 (10H), 2.66 (s, 3H), 2.61 (s, 3H), 2.15 (s, 3H), 1.62 (s, 9H), 1.56 (s, 9H), 1.53 (s, 3H), 0.93 (s, 3H), 0.31 (s, 3H), 0.58 (s, 3H), 0.51 (s, 3H), −0.26 (s, 3H), −0.39 (s, 3H).

Synthetic Example 4 (1) Preparation of Ligand Compound Synthesis of N-tert-butyl-1-(1,2-dimethyl-3H-benzo[b]cyclopenta[d]thiophene-3-yl)-1,1-(methyl)(2-methylphenyl)silanamine (i) Preparation of chloro-1-(1,2-dimethyl-3H-benzo[b]cyclopenta[d]thiophene-3-yl)-1,1-(methyl)(2-methylphenyl)silane

To a 250 ml schlenk flask, 2.0 g (1.0 eq, 9.985 mmol) of 1,2-dimethyl-3H-benzo[b]cyclopenta[d]thiophene and 50 ml of THF were put, and 4.2 ml (1.05 eq, 10.484 mmol, 2.5 M in hexane) of n-BuLi was added thereto dropwisely at −30° C., followed by stirring at room temperature overnight. A stirred Li-complex THF solution was cannulated into a schlenk flask containing 2.46 g (1.2 eq, 11.982 mmol) of dichloro(o-tolylmethyl)silane and 30 ml of THF at −78° C., followed by stirring at room temperature overnight. After stirring, drying in vacuum was carried out, and extraction with 100 ml of hexane was carried out.

(ii) Preparation of N-tert-butyl-1-(1,2-dimethyl-3H-benzo[b]cyclopenta[d]thiophene-3-yl)-1,1-(methyl)(2-methylphenyl)silanamine

After stirring 4.0 g (1.0 eq, 10.0 mmol) of the extracted chloro-1-(1,2-dimethyl-3H-benzo[b]cyclopenta[d]thiophene-3-yl)-1,1-(methyl)(2-methylphenyl)silane in 10 ml of hexane, 4.2 ml (4.0 eq, 40.0 mmol) of t-BuNH₂ was injected at room temperature, followed by stirring at room temperature overnight. After stirring, drying in vacuum was carried out, and extraction with 150 ml of hexane was carried out. After drying the solvents, 4.26 g (99%, dr=1:0.83) of a sticky liquid was obtained.

¹H-NMR (CDCl₃, 500 MHz): δ 7.95 (t, 2H), 7.70 (d, 1H), 7.52 (d, 1H), 7.47-7.44 (m, 2H), 7.24-7.02 (m, 9H), 6.97 (t, 1H), 3.59 (s, 1H), 3.58 (s, 1H), 2.50 (s, 3H), 2.44 (s, 3H), 2.25 (s, 3H), 2.16 (s, 3H), 2.06 (s, 3H), 1.56 (s, 3H), 1.02 (s, 9H), 0.95 (s, 9H), −0.03 (s, 3H), −0.11 (s, 3H).

(2) Preparation of Transition Metal Compound

To a 250 ml round flask, the ligand compound of Formula 2-3 (4.26 g, 10.501 mmol) was put in 53 ml (0.2 M) of MTBE and stirred. n-BuLi (8.6 ml, 21.52 mmol, 2.05 eq, 2.5 M in hexane) was added thereto at −40° C. and stirred at room temperature overnight.

Then, MeMgBr (8.8 ml, 26.25 mmol, 2.5 eq, 3.0 M in diethyl ether) was slowly added thereto dropwisely at −40° C., and TiCl₄ (10.50 ml, 10.50 mmol) was put in order, followed by stirring at room temperature overnight. After that, the reaction mixture was filtered using hexane.

DME (3.3 ml, 31.50 mmol) was added to the filtrate, and the resultant solution was filtered using hexane and concentrated to obtain 3.42 g (68%, dr=1:0.68) of a yellow solid.

¹H NMR (CDCl₃, 500 MHz): δ 7.83 (d, 1H), 7.80 (d, 1H), 7.74 (d, 1H), 7.71 (d, 1H), 7.68 (d, 1H), 7.37 (d, 1H), 7.31-6.90 (m, 9H), 6.84 (t, 1H), 2.54 (s, 3H), 2.47 (s, 3H), 2.31 (s, 3H), 2.20 (s, 3H), 1.65 (s, 9H), 1.63 (s, 9H), 1.34 (s, 3H), 1.00 (s, 3H), 0.98 (s, 3H), 0.81 (s, 3H), 0.79 (s, 3H), 0.68 (s, 3H), 0.14 (s, 3H), −0.03 (s, 3H).

Comparative Synthetic Example 1

The compound above was synthesized according to a method described in PCT Publication WO 2016-186295 A1 and then, used.

Preparation of Ethylene/Alpha-Olefin Copolymer Preparation Example 1

While injecting a hexane solvent in 5 kg/h and 1-butene in 1.15 kg/h, a 1.5 L continuous process reactor was pre-heated at 120° C. Triisobutylaluminum (Tibal, 0.045 mmol/min), a mixture (0.120 μmol/min) of the transition metal compounds obtained in Preparation Examples 1 and 2 in a molar ratio of 3:7, and a dimethylanilinium tetrakis(pentafluorophenyl)borate co-catalyst (0.144 μmol/min) were put in the reactor at the same time. Then, into the reactor, ethylene (0.87 kg/h) and a hydrogen gas (20 cc/min) were injected and copolymerization reaction was continuously carried out while maintaining a pressure of 89 bar and 130.1° C. for 60 minutes or more to prepare a copolymer. After drying for 12 hours or more in a vacuum oven, yield was measured, and the results are shown in Table 1.

Examples 2 to 4, and Comparative Examples 1 to 5

Ethylene/alpha-olefin copolymers were prepared by the same method as in Example 1 except for changing polymerization conditions as shown in Table 1 below.

TABLE 1 Alpha Polymerization Catalyst Molar Cat. Co-cat. Tibal C2 C6 olefin Hydrogen temp. Yield type ratio μmol/min mmol/min kg/h kg/h type kg/h cc/min ° C. g/min Preparation Synthetic 3:7 0.120 0.144 0.045 0.87 5.0 1-C4 1.15 20 130.1 10.8 Example 1 Example 1 + Synthetic Example 2 Preparation Synthetic 3:7 0.120 0.144 0.045 0.87 5.0 1-C4 1.00 20 130.5 9.9 Example 2 Example 1 + Synthetic Example 3 Preparation Synthetic 3:7 0.135 0.162 0.045 0.87 5.0 1-C4 0.70 20 130.2 9.5 Example 3 Example 1 + Synthetic Example 3 Preparation Synthetic 3:7 0.120 0.144 0.058 0.87 5.0 1-C4 0.84 22 130.9 10.8 Example 4 Example 1 + Synthetic Example 4 Comparative Comparative — 0.120 0.188 0.035 0.87 5.0 1-C4 1.15 2 130.8 12.5 Preparation Synthetic Example 1 Example 1 Comparative Synthetic 8:2 0.200 0.400 0.035 0.87 5.0 1-C4 0.70 7 132.1 13.4 Preparation Example 3 + Example 2 Comparative Synthetic Example 1 Comparative Synthetic — 0.120 0.144 0.040 0.87 5.0 1-C4 0.70 23 130.1 9.8 Preparation Example 2 Example 3 Comparative Synthetic — 0.170 0.204 0.045 0.87 5.0 1-C4 0.84 23 136.8 9.6 Preparation Example 3 Example 4 Comparative Synthetic — 0.600 2.600 0.045 0.87 5.0 1-C8 0.31 — 160.0 15.4 Preparation Example 1 Example 5

Analysis of Ethylene/Alpha-Olefin Copolymer Experimental Example 1

With respect to the ethylene/alpha-olefin copolymers prepared in the Preparation Examples and Comparative Preparation Examples, physical properties were measured by the methods below and are shown in Table 2.

(1) Density (g/cm³)

Measurement was conducted according to ASTM D-792.

(2) Melt Index (MI_(2.16), dg/min)

Measurement was conducted according to ASTM D-1238 (condition E, 190° C., 2.16 kg load).

(3) Melt Flow Rate Ratio (MFRR, MI₁₀/MI_(2.16))

MI₁₀ (condition E, 190° C., 10 kg load) and MI_(2.16) (condition E, 190° C., 2.16 kg load) were measured according to ASTM D-1238 and MI₁₀/MI_(2.16) was calculated.

(4) Melting Temperature (Tm) and Crystallization Temperature (Tc)

Melting temperature (Tm) and crystallization temperature (Tc) could be obtained using differential scanning calorimeter (DSC 6000) manufactured by PerkinElmer, and particularly, using DSC under a nitrogen atmosphere, the temperature of the copolymer was elevated to 150° C., maintained for 5 minutes, decreased to −100° C., and elevated again, and a DSC curve was observed. In this case, the temperature elevating rate and decreasing rate were 10° C./min, respectively.

In the measured DSC curve, the melting temperature was the maximum point of an endothermic peak during the second temperature elevation, and the crystallization temperature was determined as the maximum point of an exothermal peak during decreasing the temperature.

(5) Molecular Weight Distribution (MWD)

A weight average molecular weight (Mw) and a number average molecular weight (Mn) of the copolymer thus produced were measured under analysis conditions of gel permeation chromatography (GPC) below, and molecular weight distribution (MWD) was calculated from the ratio of Mw/Mn.

-   -   Column: Agilent Olexis     -   Solvent: Trichlorobenzene     -   Flow rate: 1.0 ml/min     -   Specimen concentration: 1.0 mg/ml     -   Injection amount: 200 μl     -   column temperature: 160° C.     -   Detector: Agilent High Temperature RI detector     -   Standard: Polystyrene (calibrated by cubic function)     -   Data processing: Cirrus

(6) C2 Value

Measurement was conducted using a measurement apparatus of ARES-G2 of TA Co. Particularly, a disk type disk specimen having a diameter of 25 mm and a thickness of 1 mm was prepared as the sample of an ethylene/alpha-olefin copolymer. The geometry of a parallel plate (flat shape) was used, and Equation 1 was calculated by the methods 1) and 2) below.

1) Frequency Sweep at Five Specific Temperatures

In a temperature range lower than Tg+200° C. of an ethylene/alpha-olefin copolymer, frequency sweep was measured at five specific temperatures selected with an interval of 10° C. In the present invention, measurement was conducted at a temperature of 110-150° C. with an interval of 10° C. (strain 0.5-3%, frequency 0.1-500 rad/s).

2) Deduction of Master Curve

The reference temperature T_(r) was set to 130° C., and the measurement results of step 1) at 130° C. was shifted to deduce a master curve.

3) Deduction of C₂ Value

The shift factor (aT) of a WLF equation was obtained, and this value was substituted in Equation 2 to deduce a C₂ value.

TABLE 2 Density MI MFRR Tm Tc MWD C2 g/cm³ dg/min — ° C. ° C. — — Preparation 0.878 5.8 6.2 64.1 47.0 1.98 403 Example 1 Preparation 0.878 4.3 6.1 64.2 48.3 2.00 498 Example 2 Preparation 0.878 4.8 6.0 62.1 46.9 1.97 488 Example 3 Preparation 0.877 6.1 6.1 62.2 47.5 2.00 449 Example 4 Comparative 0.878 5.0 7.3 62.8 47.7 2.23 625 Preparation Example 1 Comparative 0.875 4.0 6.7 90.4 67.0 2.35 423 Preparation Example 2 Comparative 0.878 5.6 5.9 62.0 47.5 1.96 646 Preparation Example 3 Comparative 0.879 4.5 6.1 63.4 49.3 2.01 610 Preparation Example 4 Comparative 0.902 4.2 7.4 103.0 78.1 2.24 470 Preparation Example 5

As summarized in Table 2, it was confirmed that Preparation Examples 1 to 4 corresponding to the ethylene/alpha-olefin copolymers according to the present invention showed small C2 values of 500 or less and narrow molecular weight distribution and also satisfied the ranges of the density and the melting temperature defined in the present invention. On the contrary, the ethylene/alpha-olefin copolymers of Comparative Examples 1, 3 and 4 showed high C2 values greater than 600, and this indicates that the crystallinity distribution of the copolymers was narrow, and free volume ratios were high. In addition, it was confirmed that the molecular weight distribution and melting temperature of the copolymer of Comparative Preparation Example 2 were high and deviated from the ranges of the present invention, and the density and melting temperature of the copolymer of Comparative Preparation Example 5 deviated from the ranges of the present invention.

Manufacture of Encapsulant Film Example 1

To 500 g of the sample of Preparation Example 1, 1 phr (parts per hundred rubber) of t-butyl 1-(2-ethylhexyl)monoperoxycarbonate (TBEC), 0.5 phr of triallylisocyanurate (TAIL), and 0.2 phr of methacryloxypropyltrimethoxysilane (MEMO) were injected to prepare a composition for an encapsulant film. Then, soaking was performed at 40° C. for 1 hour, and aging was performed for 15 hours.

After that, an encapsulant film having an average thickness of 550 μm was manufactured at a low temperature to a degree not achieving high-temperature crosslinking (conditions of 100° C. or less of extruder barrel temperature) using a micro extruder.

Examples 2 to 4, and Comparative Examples 1 to 5

Encapsulant films were manufactured by the same method as in Example 1 except for using the copolymers of Preparation Examples 2 to 4, and Comparative Preparation Examples 1 to 5 as samples, respectively.

Analysis of Encapsulant Film Experimental Example 2

Between two release films (thickness: about 100 μm), the encapsulant film (15 cm×15 cm) with a thickness of 550 μm thus manufactured was put and crosslinked by lamination in a vacuum laminator at a process temperature of 150° C. for a process time of 19 minutes and 30 seconds (vacuum for 5 minutes/pressurizing for 1 minute/keeping pressure for 13 minutes and 30 seconds).

Then, volume resistance and light transmittance were measured by the methods below and recorded in Table 3 below.

(1) Volume Resistance

Measurement was conducted by applying a voltage of 1000 V for 60 seconds using Agilent 4339B High-resistance meter (product of Agilent Technologies K.K.) under temperature conditions of 23±1° C. and humidity conditions of 50%±3.

(2) Light Transmittance

Light transmittance at 550 nm was measured using Shimadzu UV-3600 spectrophotometer.

-   -   measurement mode: transmittance     -   wavelength interval: 1 nm     -   measurement rate: medium

TABLE 3 Volume resistance Light transmittance (Ω · cm) (%) Example 1 4.0 × 10¹⁵ 91.3 Example 2 3.5 × 10¹⁵ 91.5 Example 3 3.5 × 10¹⁵ 91.2 Example 4 5.0 × 10¹⁵ 91.7 Comparative Example 1 7.0 × 10¹⁴ 91.1 Comparative Example 2 1.5 × 10¹⁵ 88.7 Comparative Example 3 8.0 × 10¹⁴ 91.3 Comparative Example 4 8.5 × 10¹⁴ 91.4 Comparative Example 5 2.0 × 10¹⁵ 88.3

As shown in the table, it was confirmed that the encapsulant films of the Examples according to the present invention achieved both high volume resistance and high light transmittance in contrast to the Comparative Examples. Particularly, since the encapsulant films of Comparative Examples 1, 3 and 4 included the ethylene/alpha-olefin copolymers having a C2 value greater than 600, largely degraded volume resistance was shown, and the encapsulant films of Comparative Examples 2 and 5 showed particularly low light transmittance. Like this, if an encapsulant film is manufactured using an ethylene/alpha-olefin copolymer satisfying the density, molecular weight distribution, melting temperature and C2 value defined in the present invention, excellent levels of volume resistance and light transmittance may be achieved without using a separate additive.

Manufacture and Analysis of Solar Cell Module Experimental Example 3

A solar cell module was manufactured using each of the encapsulant films (thickness of 500 μm) of Examples 2 and 4, and Comparative Examples 3 and 4, a fluorine-based back sheet, low iron tempered glass and a crystalline silicon solar cell. A solar cell module was manufactured by reducing the pressure of the arranged inside of the module at 150° C. conditions for 20 minutes using a vacuum laminator.

(1) Evaluation of Potential Induced Degradation (PID)

With respect to the solar cell module thus manufactured, initial output was measured, and after 288 hours at 85° C., 85% RH, and under −1,000 V, loss rate (%) in contrast to the initial output was calculated.

TABLE 4 Loss rate in contrast to initial output (%) Example 2 0.6 Example 4 0.4 Comparative Example 3 7.0 Comparative Example 4 8.0

As described above, it could be found that since the volume resistance of the encapsulant film according to the present invention is excellent, if a solar cell module is manufactured using the same, the degradation of output due to PID phenomenon is largely prevented. 

1. A composition for an encapsulant film, the composition comprising an ethylene/alpha-olefin copolymer satisfying the following conditions (a) to (d): (a) a density is 0.85 to 0.89 g/cc; (b) a molecular weight distribution is 1.5 to 2.3; (c) a melting temperature is 85° C. or less; and (d) a free volume proportional constant (C₂) derived from the following Equations 1 and 2 is 600 or less: $\begin{matrix} {{\log\frac{\eta_{0}(T)}{\eta_{0}\left( T_{r} \right)}} = {\log\left( a_{T} \right)}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack \end{matrix}$ in Formula 1, η₀(T) is a viscosity (Pa·s) of a copolymer measured at an arbitrary temperature of T (K) using ARES-G2 (Advanced Rheometric Expansion System), η₀(T_(r)) is a viscosity (Pa·s) of a copolymer measured at a reference temperature of T_(r) (K) using the ARES-G2, and a_(T) is a shift factor of the arbitrary temperature of T (K) with respect to the reference temperature of T_(r) (K), and obtained from Equation 1 above, $\begin{matrix} {{\log\left( a_{T} \right)} = \frac{- {C_{1}\left( {T - T_{r}} \right)}}{C_{2}\left( {T - T_{r}} \right)}} & \left\lbrack {{Equation}\mspace{14mu} 2} \right\rbrack \end{matrix}$ in Formula 2, C₁ is a free volume inverse proportional constant, C₂ is a free volume proportional constant (K), and C₁ and C₂ are intrinsic constants of the ethylene/alpha-olefin copolymer, and obtained from Equation 2 above.
 2. The composition for an encapsulant film according to claim 1, wherein the C2 is 300 to
 550. 3. The composition for an encapsulant film according to claim 1, wherein the molecular weight distribution of the ethylene/alpha-olefin copolymer is 1.8 to 2.2.
 4. The composition for an encapsulant film according to claim 1, wherein a melt flow rate ratio (MFRR, MI₁₀/MI_(2.16)) which is a value of a melt index (MI₁₀, 190° C., 10 kg load conditions) with respect to a melt index (MI_(2.16), 190° C., 2.16 kg load conditions) of the ethylene/alpha-olefin copolymer is 8.0 or less.
 5. The composition for an encapsulant film according to claim 1, wherein a crystallization temperature of the ethylene/alpha-olefin copolymer is 70° C. or less.
 6. The composition for an encapsulant film according to claim 1, wherein a melt index (MI_(2.16), 190° C., 2.16 kg load conditions) of the ethylene/alpha-olefin copolymer is 0.1 to 50 dg/min.
 7. The composition for an encapsulant film according to claim 1, wherein a weight average molecular weight of the ethylene/alpha-olefin copolymer is 40,000 to 150,000 g/mol.
 8. The composition for an encapsulant film according to claim 1, wherein the alpha-olefin comprises one or more selected from the group consisting of propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, 1-octene, 1-decene, 1-undecene, 1-dodecene, 1-tetradecene, 1-hexadecene and 1-eicosene.
 9. The composition for an encapsulant film according to claim 1, wherein the alpha-olefin is comprised in greater than 0 to 99 mol % with respect to the ethylene/alpha-olefin copolymer.
 10. The composition for an encapsulant film according to claim 1, further comprising one or more selected from the group consisting of a crosslinking agent, a crosslinking auxiliary agent, a silane coupling agent, an unsaturated silane compound, an amino silane compound, a light stabilizer, a UV absorbent and a thermal stabilizer.
 11. An encapsulant film comprising the composition for an encapsulant film according to claim
 1. 12. A solar cell module comprising the encapsulant film of claim
 11. 13. A method for preparing the composition for an encapsulant film according to claim 1, the method comprising polymerizing ethylene and an alpha-olefin-based monomer in the presence of a catalyst composition including a transition metal compound represented by the following Formula 1 and a transition metal compound represented by the following Formula 2 to prepare the ethylene/alpha-olefin copolymer; and mixing the ethylene/alpha-olefin copolymer with a crosslinking agent, a crosslinking auxiliary agent and a silane coupling agent,

in Formula 1, R₁ is hydrogen; alkyl of 1 to 20 carbon atoms; cycloalkyl of 3 to 20 carbon atoms; alkenyl of 2 to 20 carbon atoms; alkoxy of 1 to 20 carbon atoms; aryl of 6 to 20 carbon atoms; arylalkoxy of 7 to 20 carbon atoms; alkylaryl of 7 to 20 carbon atoms; or arylalkyl of 7 to 20 carbon atoms, R₂ and R₃ are each independently hydrogen; halogen; alkyl of 1 to 20 carbon atoms; cycloalkyl of 3 to 20 carbon atoms; alkenyl of 2 to 20 carbon atoms; arylalkyl of 7 to 20 carbon atoms; alkylamido of 1 to 20 carbon atoms; or arylamido of 6 to 20 carbon atoms, R₄ and R₅ are each independently hydrogen; alkyl of 1 to 20 carbon atoms; cycloalkyl of 3 to 20 carbon atoms; aryl of 6 to 20 carbon atoms; or alkenyl of 2 to 20 carbon atoms, R₆ to R₉ are each independently hydrogen; alkyl of 1 to 20 carbon atoms; cycloalkyl of 3 to 20 carbon atoms; aryl of 6 to 20 carbon atoms; or alkenyl of 2 to 20 carbon atoms, or two or more adjacent groups among R₆ to R₉ are optionally connected with each other to form a ring, Q₁ is Si, C, N, P or S, M₁ is Ti, Hf or Zr, and X₁ and X₂ are each independently hydrogen; halogen; alkyl of 1 to 20 carbon atoms; alkenyl of 2 to 20 carbon atoms; aryl of 6 to 20 carbon atoms; alkylaryl of 7 to 20 carbon atoms; arylalkyl of 7 to 20 carbon atoms; alkylamino of 1 to 20 carbon atoms; or arylamino of 6 to 20 carbon atoms,

in Formula 2, R₁₀ is hydrogen; alkyl of 1 to 20 carbon atoms; cycloalkyl of 3 to 20 carbon atoms; alkenyl of 2 to 20 carbon atoms; alkoxy of 1 to 20 carbon atoms; aryl of 6 to 20 carbon atoms; arylalkoxy of 7 to 20 carbon atoms; alkylaryl of 7 to 20 carbon atoms; or arylalkyl of 7 to 20 carbon atoms, R_(11a) to R_(11e) are each independently hydrogen; halogen; alkyl of 1 to 20 carbon atoms; cycloalkyl of 3 to 20 carbon atoms; alkenyl of 2 to 20 carbon atoms; alkoxy of 1 to 20 carbon atoms; or aryl of 6 to 20 carbon atoms, R₁₂ is hydrogen; halogen; alkyl of 1 to 20 carbon atoms; cycloalkyl of 3 to 20 carbon atoms; alkenyl of 2 to 20 carbon atoms; aryl of 6 to 20 carbon atoms; alkylaryl of 7 to 20 carbon atoms; arylalkyl of 7 to 20 carbon atoms; alkylamido of 1 to 20 carbon atoms; or arylamido of 6 to 20 carbon atoms, R₁₃ and R₁₄ are each independently hydrogen; alkyl of 1 to 20 carbon atoms; cycloalkyl of 3 to 20 carbon atoms; aryl of 6 to 20 carbon atoms; or alkenyl of 2 to 20 carbon atoms, R₁₅ to R₁₈ are each independently hydrogen; alkyl of 1 to 20 carbon atoms; cycloalkyl of 3 to 20 carbon atoms; aryl of 6 to 20 carbon atoms; or alkenyl of 2 to 20 carbon atoms, or two or more adjacent groups among R₁₅ to R₁₈ are optionally connected with each other to form a ring, Q₂ is Si, C, N, P or S, M₂ is Ti, Hf or Zr, and X₃ and X₄ are each independently hydrogen; halogen; alkyl of 1 to 20 carbon atoms; alkenyl of 2 to 20 carbon atoms; aryl of 6 to 20 carbon atoms; alkylaryl of 7 to 20 carbon atoms; arylalkyl of 7 to 20 carbon atoms; alkylamino of 1 to 20 carbon atoms; or arylamino of 6 to 20 carbon atoms.
 14. The method according to claim 13, wherein a molar ratio of the transition metal compound represented by Formula 1 and the transition metal compound represented by Formula 2 is 1:1.2 to 1:10.
 15. The method according to claim 13, wherein hydrogen is injected at 5 to 100 cc/min. 